A bi-directional fixating transvertebral (BDFT) screw/cage apparatus includes an intervertebral cage having a plurality of internal angled screw guides and screw members and a screw locking mechanism. The screw locking mechanism has leaf springs mechanically interacting with ratcheted screw heads of the screws and allowing the ratchet teeth of the screw heads to rotate only in a penetrating direction and preventing rotation of the screw head in an opposite direction. The intervertebral cage is adapted for posterior lumbar intervertebral placement, anterior lumbar intervertebral placement, anterio-lateral thoracic intervertebral placement, or anterior cervical intervertebral placement.Related Terms:AnteriorCervicalLumbarPosteriorThoracicVertebraIntervertebral CageVertebral Body

This application is a Continuation-In-Part Application, for which priority is claimed under 35 U.S.C. §120, of copending U.S. patent application Ser. No. 13/103,994, filed on May 9, 2011 (Attorney Docket No. 3003/0107PUS8), which is a Divisional of U.S. patent application Ser. No. 12/054,335, filed on Mar. 24, 2008 (now U.S. Pat. No. 7,972,363 B2, issued on Jul. 5, 2011) (Attorney Docket No. 3003/0107PUS1), which is a Continuation-In-Part of copending application Ser. No. 11/842,855, filed on Aug. 21, 2007 (now U.S. Pat. No. 7,942,903, issued May 17, 2011) (Attorney Docket No. 3003/0105PUS1), which is a Continuation-In-Part of application Ser. No. 11/536,815, filed on Sep. 29, 2006 (now U.S. Pat. No. 7,846,188 B2, issued Dec. 7, 2010) (Attorney Docket No. 3003/0104PUS2), which is a Continuation-In-Part of application Ser. No. 11/208,644, filed on Aug. 23, 2005 (now U.S. Pat. No. 7,704,279 issued on Apr. 27, 2010) (Attorney Docket No. 3003/0104PUS1), the entire contents of all of the above identified patent applications are hereby incorporated by reference in their entirety and for which priority of each of the above-identified applications is claimed under 35 U.S.C. §120.

This application also is a Continuation-In-Part Application, for which priority is claimed under 35 U.S.C. §120, of copending application Ser. No. 13/084,543, filed on Apr. 11, 2011 (Attorney Docket No. 3003/0105PUS2), which is a Divisional of copending application Ser. No. 11/842,855, filed on Aug. 21, 2007 (now U.S. Pat. No. 7,942,903, issued May 17, 2011) (Attorney Docket No. 3003/0105PUS1), which is a Continuation-In-Part of application Ser. No. 11/536,815, filed on Sep. 29, 2006 (now U.S. Pat. No. 7,846,188 B2, issued Dec. 7, 2010) (Attorney Docket No. 3003/0104PUS2), which is a Continuation-In-Part of application Ser. No. 11/208,644, filed on Aug. 23, 2005 (now U.S. Pat. No. 7,704,279 issued on Apr. 27, 2010) (Attorney Docket No. 3003/0104PUS1), the entire contents of all of the above identified patent applications are hereby incorporated by reference in their entirety and for which priority of each of the above-identified applications is claimed under 35 U.S.C. §120.

This application also is a Continuation-In-Part Application, for which priority is claimed under 35 U.S.C. §120, of copending application Ser. No. 13/401,829, filed on Feb. 21, 2012 (Attorney Docket No. 3003/0107PUS5), which claims priority under 35 U.S.C. §119(e) of U.S. Provisional Application No. 61/445,034, filed on Feb. 21, 2011 (Attorney Docket No. 3003/0107PR05), the entire contents of all of the above identified patent applications are hereby incorporated by reference in their entirety.

The present invention relates to a unique universal bi-directional screw (BDS) system, and in particular its application to the spine, also referred to as bi-directional fixating transvertebral (BDFT) screw/cage constructs which can be used as stand-alone intervertebral devices which combine the dual functions of an intervertebral spacer that can be filled with bone fusion material(s), as well as a bi-directional transvertebral bone fixating/fusion screw apparatus. In the posterior lumbosacral and thoracic spine, intervertebral cage/BDFT screw constructs can be used as stand-alone devices obviating the need for pedicle screw fixation in many but not all cases. In the anterior cervical, thoracic and lumbosacral spine, intervertebral cage/BDFT screw constructs can be used as stand-alone devices obviating the need for anterior or lateral (thoracic and lumbosacral) spinal plating, and/or supplemental posterior pedicle screw fixation.

BACKGROUND

The history and evolution of instrumented spinal fusion in the entire human spine has been reviewed in related applications Ser. No. 12/054,335, filed on Mar. 24, 2008, Ser. No. 13/084,543, filed on Apr. 11, 2011, Ser. No. 11/842,855, filed on Aug. 21, 2007, Ser. No. 11/536,815, filed on Sep. 29, 2006, and Ser. No. 11/208,644, filed on Aug. 23, 2005, the contents of which are hereby incorporated by reference in their entirety. Conventionally, the majority of posterior cervical and almost all posterior thoracic and lumbosacral fusion surgical techniques are typically supplemented with pedicle screw placement. Conventionally, the majority of anterior cervical spinal fusions, and many anterio-lateral thoracic, and anterior or anterio-lateral lumbosacral fusions are supplemented with anterior or anterior-lateral spinal plating, and very often, in particular in the thoracic and lumbosacral spine, are supplemented with posterior pedicle screw instrumentation.

Complications of pedicle screw placement in cervical, thoracic and lumbosacral spine include duration of procedure, significant tissue dissection and muscle retraction, misplaced screws with neural and/or vascular injury, excessive blood loss, need for transfusions, prolonged recovery, incomplete return to work, and excessive rigidity leading to adjacent segmental disease requiring further fusions and re-operations. Recent advances in pedicle screw fixation including minimally invasive, and stereotactic CT image-guided technology, and the development of flexible rods, imperfectly address some but not all of these issues.

Complications of anterior plating in the cervical spine include potential plate, and/or screw esophageal compression, and misplaced screws leading to neurovascular injury. Complications of anterior or anterior-lateral plating in the anterior lumbar spine include potential devastating injury to the major vessels due to chronic vascular erosion of the major vessels, or acute vascular injuries due to partial or complete plate and/or screw back out. Furthermore, for re-do surgeries, plate removal can be arduous, with potential complications of prolonged esophageal retraction, vascular injury and screw breakage. Recent advances including diminishing the plate width and/or profile, and absorbable plates, imperfectly address some but not all of these issues.

Complications of all conventional spinal anterior intervertebral device constructs are their potential for extrusion in the absence of plating. Hence, they are supplemented with anterior plating to prevent extrusion. Complications of posterior lumbosacral intervertebral device construct in the presence or absence of supplemental pedicle screw fixation is device extrusion, and potential nerve root and/or vascular injuries.

SUMMARY

Herein described are multiple exemplary embodiments of a device which combines in a single stand-alone construct the dual functions of: a) an intervertebral cage spacer which can be filled with bone fusion material maintaining disc height, and, b) a bi-directional fixating/fusion transvertebral body screw apparatus. These embodiments are described for posterior and anterior lumbar (and anterio-lateral thoracic) intervertebral placement, and anterior cervical intervertebral placement. The present invention recognizes the aforementioned problems with prior art apparatus and solves these problems by, among other things, improving upon the designs illustrated in the aforementioned related applications. The present application provides an advanced and novel bi-directional fixating transvertebral (BDFT) screw/cage apparatus with a modified novel cage which has indentations on the upper aspect of the screw box adjacent to the internalized angled screw guides. These indentations have leaf springs which are press fit into these indentations. The leaf springs function as screw locking mechanisms in conjunction with specialized BDFT screws that are designed with ratcheted screw heads. The small leaf springs which are perpendicularly aligned with the screw head ratchet spiked teeth and troughs allow the ratchet teeth of the screw heads to rotate only in the penetrating direction. Due to the geometric orientation of the ratchet teeth and troughs vis-à-vis the spring leaf, rotation of the screw head in the opposite direction is prevented. The spring leaf engages the space between the ratchet teeth (troughs) upon its final allowed turn, and prevents any rotation in the opposite direction thereby locking the screw into its final position. The interaction between the adjacent leaf springs and the screws ratcheted teeth and troughs which only allow screw rotation in the penetrating direction is the mechanical basis for this novel locking mechanism. This mechanism can be used not only for these constructs but also with any other device which requires a locking screw. All these novel modifications improve the probability of a solid fusion with this new invention.

The exemplary embodiments of a bi-directional fixating transvertebral (BDFT) screw/cage apparatus provide as strong or stronger segmental fusion as pedicle screws without the complications arising from pedicle screw placement, which include misplacement with potential nerve and/or vascular injury, violation of healthy facets, possible pedicle destruction, blood loss, and overly rigid fusions. By placing screws across the intervertebral space from vertebral body to vertebral body, engaging anterior and middle spinal columns and not the vertebral bodies via the transpedicular route thereby excluding the posterior spinal column, then healthy facet joints, if they exist, are preserved. Because the present invention accomplishes both anterior and middle column fusion, without rigidly fixating the posterior column, the present invention in essence creates a flexible fusion.

The present invention recognizes that the very advantage of transpedicular screws which facilitate a strong solid fusion by rigidly engaging all three spinal columns is the same mechanical mechanism whereby complete inflexibility of all columns is incurred thereby leading to increasing rostral and caudal segmental stress which leads to an increased rate of re-operation.

Transvertebral fusion also leads to far less muscle retraction, blood loss and significant reduction in operating room (O.R.) time. Thus, the complication of pedicle screw pull out, and hence, high re-operation rate associated with the current embodiment of flexible fusion pedicle screws/rods is obviated. The lumbosacral intervertebral cage/BDFT screw constructs can be introduced via posterior, lateral, transforaminal or anterior interbody fusion approaches/surgical techniques. Although one can opt to supplement these constructs with transpedicular screws there would be no absolute need for supplemental pedicle screw fixation with these operative techniques.

The anterior placement of a bi-directional fixating transvertebral (BDFT) screw/cage apparatus according to the embodiments of the present invention into the cervical and lumbar spine obviates the need for supplemental anterior cervical or anterior lumbar plating. The sole purpose of these plates is to prevent intervertebral device extrusion. This function is completely obviated and replaced by the dual functioning bi-directional fixating transvertebral (BDFT) screw/cage apparatus, according to the present invention. The obvious advantage of this is a significant savings in operative time, and prevention of injuries associated with plating, in particular esophageal, large and small vessel injuries, and spinal cord nerve root injuries.

Because the embodiments of the bi-directional fixating transvertebral (BDFT) screw/cage apparatus engage a small percentage of the rostral and caudal vertebral body surface area, multi-level fusions can be performed with these devices.

Likewise, anterior cervical intervertebral cage/BDFT screw construct placement can be used to salvage failed anterior cervical arthroplasties, and re-do fusions without having to supplement with cervical anterior plates, thereby reducing the morbidity of this procedure.

In addition, if a patient develops a discogenic problem necessitating anterior cervical discectomy and fusion at a level above or below a previously fused and plated segment, the present invention reduces or eliminates the need to remove the prior plate in order to place a new superior plate, because the function of the plate is replaced by the dual functioning intervertebral cervical construct, thereby reducing the operating room time and surgical morbidity of this procedure.

Furthermore, because of the orientation and length of the BDFT screws within the intervertebral cage/BDFT constructs, multiple level fusions can be easily performed.

For example, an exemplary embodiment is directed to an intervertebral cage spacer and bi-directional fixating/fusion transvertebral body screw/cage apparatus. The apparatus includes an intervertebral cage for maintaining disc height. The intervertebral cage includes a first internal screw guide and a second internal screw guide adjacent to novel cage indentations which contains a press-fit leaf spring. The apparatus further includes a first screw member having a screw head with ratchet teeth, a tapered end and a threaded body disposed within the intervertebral cage, a second screw member having a screw head with ratchet teeth, a tapered end and a threaded body disposed within the intervertebral cage, and a first screw locking mechanism that prevents the first screw member and the second screw from pulling-out of the first internal screw guide and the second internal screw guide.

Another exemplary embodiment is directed to an integral intervertebral cage spacer and bi-directional fixating/fusion transvertebral body screw apparatus, including an intervertebral cage having a plurality of internal angled screw guides. The apparatus further includes a plurality of screw members having a screw head with ratchet teeth and troughs, a tapered end and a threaded body disposed within the plurality of internal angled screw guides of the intervertebral cage, which are adjacent to novel cage indentations which contain press fit leaf springs. Due to the geometric orientation of the ratchet teeth on the screw head, the adjacent leaf springs allow the screws to rotate only in the penetrating direction. Screw rotation in the opposite, back out, direction is prevented because the leaf spring engages the space in between the ratchet teeth (troughs) preventing this opposite rotation and hence locking it preventing the plurality of screw members from pulling out of the plurality of internal angled screw guides.

Another exemplary embodiment is directed to a method of inserting a bi-directional fixating transvertebral (BDFT) screw/cage apparatus between a first vertebral body and a second vertebral body. The method includes measuring a dimension of a disc space between the first vertebral body and the second vertebral body, determining that the disc space is a posterior or lateral lumbar disc space, an anterior lumbar disc space, or an anterior cervical disc space, selecting an intervertebral cage based on the measured dimension of the disc space and based on the determination of the disc space being the posterior lumbar disc space, the lateral lumbar disc space, the anterior lumbar disc space, or the anterior cervical disc space, inserting the selected intervertebral cage into a midline of the disc space until the selected intervertebral cage is flush or countersunk relative to the first vertebral body and the second vertebral body, inserting a first screw member into a first internal screw guide of the selected intervertebral cage, inserting a second screw member into a second internal screw guide of the selected intervertebral cage, screwing the first screw member and the second screw member into the first vertebral body and the second vertebral body respectively, confirming a position and placement of the intervertebral cage relative to the first vertebral body and the second vertebral body, and locking the first screw member and the second screw member in a final position by its final turn when it's flush with the surface of the cage. The leaf spring prevents screw back out or pull out by engaging and locking the space between the ratchet teeth (troughs) of the screw head when the screws are in their final resting positions.

The posterior lumbar BDFT cage screw apparatus is uniquely designed in order to get into the posterior space and obtain proper screw angulations. Two exemplary embodiments are described; one that is rectangular and one that is elliptical and concave mimicking the posterior intervertebral disc space. In both exemplary embodiments, the axes of the internal screw guides are not horizontally aligned as they are in the cervical embodiment. Their axes must be oblique one to the other, and the screw guides must be very close to one another, in order for the screws to achieve proper vertebral body penetration in such a restricted posterior lumbar inter space.

In the embodiments having an anterior lumbar embodiment four screw design, in order to achieve maximal stability and to prevent subsidence, the lateral two screws penetrate the inferior vertebral body, and the middle two screws project to the superior vertebral body.

In all BDFT embodiments, the screw angle guides have an approximate twenty five degree angle. The angles can be variable or divergent.

In all embodiments the screw drill guide narrows such that the screw head is countersunk into the cage and thus it can be locked even in the absence of an additional screw locking mechanism. The screw locking mechanism described herein is yet an additional mechanism preventing screw back out.

DETAILED DESCRIPTION

Aspects of the invention are disclosed in the following description and related drawings directed to specific embodiments of the invention. Alternate embodiments may be devised without departing from the scope of the invention. Additionally, well-known elements of the invention will not be described in detail or will be omitted so as not to obscure the relevant details of the invention.

The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Likewise, the term “embodiments of the invention” does not require that all embodiments of the invention include the discussed feature, advantage or mode of operation.

With reference to FIGS. 1A-5E, exemplary embodiments of the invention will now be described.

1. Exemplary Medical Device

Referring to FIGS. 1A-5E the above described problems of the conventional art can be solved in the cervical, thoracic and lumbosacral spines by insertion into the denuded intervertebral disc space multiple embodiments of a bi-directional fixating transvertebral (BDFT) screw/cage apparatus.

For example, FIGS. 1A-1G illustrate three-dimensional views of an exemplary embodiment of an anterior cervical intervertebral cage/BDFT construct 10. In this embodiment, the top portion of the cage 10 has indentations 70 that are adjacent to the internalized screw guides 80, 90 (FIG. 1F) which contain press-fit leaf spring screw locking mechanisms 20. The cage 10 also includes additional indentations 12 on the side surfaces of the cage 10 for insertion of the prongs of an insertion device. In an exemplary embodiment, a side surface of the cage 10 can elliptically contoured when viewed from the side (FIG. 1C) to fit into the bi-concave cervical disc space. The embodiment includes two screws 30, 40. The screws 30, 40 include screw heads with ratchet teeth. The teeth have troughs in between. A first screw 30 is oriented rostrally (superiorly) and a second screw 40 is oriented caudally (inferiorly). The cage 10 can include a cavity 60 for bone product placement. The cage 10 includes two built in internalized screw/drill guides 80, 90 (e.g., approximately having a 25 degree angulation), one for each screw 30, 40, which orient the screws 30, 40 bi-directionally in opposite directions. The cage 10 can include a screw guide tunnel exit 13 adjacent to the bone cavity 60 (FIG. 1). One of ordinary skill in the art will recognize that the internalized screw/drill guides 80, 90 can have different degrees of angulation and/or different positions within the cage 10.

In an embodiment, the cage includes at least one screw guide 80 or 82 having a predetermined trajectory (e.g., preferably having a 25 degree angulation) that may make placement of all screws equally facile, more amenable to multi-level placement, and may diminish the need for external drill guides. In other embodiments, the cage includes at least two screw guides 80, 82 having a predetermined trajectory (e.g., preferably having a 25 degree angulation) that may make placement of all screws equally facile, more amenable to multi-level placement, and may diminish the need for external drill guides. In other embodiments, the cage can include a screw guide 80, 82 having another predetermined trajectory, such as an angulation of substantially 25 degrees (e.g., an angulation ranging from 20 degrees to 30 degrees). In other embodiments, the cage can include a screw guide 80, 82 having another predetermined trajectory, such as an angulation ranging from 20 degrees to 25 degrees, an angulation ranging from 25 degrees to 30 degrees, an angulation ranging from 25 degrees to 35 degrees, an angulation ranging from 25 degrees to 35 degrees, an angulation ranging from 20 degrees to 40 degrees, an angulation ranging from 25 degrees to 40 degrees, etc. The embodiments of the cage can include one or more screw/drill guides 80, 82 having different angles and/or different positions within the cage.

The built in tunnels of the screw guides 80, 90 provide an important advantage of ensuring that only one prescribed angled trajectory is possible for transvertebral screw placement. The built in tunnels narrow going downward. This facilitates the locking of the screw head to the top of the cage 10 even in the absence of the locking mechanism described herein. Embodiments of the intervertebral cages 10 can be designed with internalized screw/drill guides 80, 90 with different angles and/or different positions within the cage 10. The angle and size of the screws 30, 40 make them amenable to single or multi-level placement. The superior and inferior surfaces or edges of the lumbar cage 10 can include ridges 50 or the like to facilitate integration and fusion with superior and inferior vertebral bodies.

The embodiment can include a leaf spring 20 which can be, for example, press-fit into the indentation 70 adjacent to the self-drilling internal screw guides, 80, 90 on top of the cage 10. The leaf spring 20 can be manufactured from a variety of materials, such as titanium. When the screws 30, 40 with ratcheted screw heads are turned, the first screw member 30 and the second screw member 40 are locked in a final position by its final turn when the screw head is flush with the surface of the cage 10. The adjacent leaf spring 20 prevents screw back out or pull out by engaging and locking the space between the ratchet teeth (trough) of the screw head when the screws 30, 40 are in their final resting positions. This engagement prevents any rotation of the screw 30, 40 in the opposite direction.

The exemplary embodiments of the locking mechanism are an evolutionary advance and improvement compared to the apparatus illustrated in the aforementioned related applications. The novel embodiments are quite unique and different from all other conventional screw locking mechanisms.

FIGS. 2A-2G illustrate three-dimensional views of an exemplary embodiment of an anterior lumbar intervertebral cage/BDFT construct. In this embodiment, the cage 110 includes indentations 194 on top of the cage 10 laterally adjacent to all four internalized screw guides 190, 192 (FIG. 2G), which contain press-fit leaf springs 120. The cage 110 also can include indentations 12 on both side surfaces for insertion of prongs of an implantation tool. This cage 110 can be larger than the cervical cage 10 and also can include elliptically contoured sidewalls when view from the side to fit into the bi-concave lumbar disc space (FIG. 2D). The cage 110 includes four (4) horizontally aligned internalized screw guides 190, 192 for four (4) screws 130, 140, 150, 160. The two lateral (left and right) screws 130, 160 are oriented inferiorly, and the two middle screws 140, 150 are oriented superiorly. The axes of these guides 190, 192 and screws 130, 140, 150, 160 are not perfectly horizontal with respect to each other. Each lateral screw guide/screw is obliquely oriented with respect to its adjacent medial screw guide/screw. This is necessary to achieve the proper trajectory for bone penetration along with the precise angle of the screw guides. The screw guide tunnel exits 13 are illustrated in FIG. 2C and are in continuity (connected) with the enlarged bone cavity 180. In the embodiment, the orientations of the four screw guides 190, 192 (and screws; 130, 140, 150, 160) are selected because of their symmetry and inherent stability.

The cage 110 can include a large cavity 180 for bone product placement. The cage 110 includes four built-in internalized screw/drill guides 190, 192 (e.g., having an approximate 25 degree angulation), one for each screw 130, 140, 150, 160. Other embodiments of the intervertebral cage 110 can be designed with internalized screw/drill guides 190, 192 with different angles and/or different positions within the cage 110. The angle and size of the screws 130, 140, 150, 160 make them amenable to single or multi-level placement. The superior and inferior surfaces or edges of the cage 110 can include ridges 170 or the like to facilitate integration and fusion with superior and inferior vertebral bodies. In an embodiment, there are no compartmental divisions in the cavity 180 for bone product placement to maximize the quantity of bone for fusion.

The cage 110 includes four leaf springs 120 that can be, for example, press-fit to the indentations 194 adjacent to the internalized screw guides 190, 192 on top of the cage 110 (FIG. 2). In the embodiment, the cage 110 includes one leaf spring locking mechanism 120 per screw 130, 140, 150, 160. However, in other embodiments, one locking mechanism 120 can be provided for each screw 130, 140, 150, 160, or one locking mechanism 120 can be provided for two or more screws 130, 140, 150, 160. The top of the cage 110 includes an indentation 194 for each leaf spring locking mechanism 120. Each leaf spring locking mechanism 120 also can be designed to rest and be press-fit into the indentations 194, which are adjacent to the in-built self drilling screw guides 190, 192. The leaf spring locking mechanism 120 can be manufactured from a variety of materials, such as titanium.

When each of the screws 130, 140, 150, 160 with ratcheted screw heads are turned, the screws 130, 140, 150, 160 are locked in a final position by its final turn when the screw head is flush with the surface of the cage 110. The adjacent leaf spring 120 prevents screw back out or pull out by engaging and locking the space between the ratchet teeth of the screw head (trough) when the screws 130, 140, 150, 160 are in their final resting positions. This engagement prevents any rotation of the screw 130, 140, 150, 160 in the opposite direction. It should also be noted that because of the narrowing of the screw guide tunnel 190, 192, when the screw head is countersunk into the top of the cage 110, this also serves as a preliminary locking mechanism.

The exemplary embodiments are an evolutionary advance and improvement compared to the apparatus illustrated in the aforementioned related applications, and are quite unique and different from all other conventional locking mechanisms used for other types of anterior lumbar cages.

A possible conventional device conceivably may include anterior placed lumbar implants with perforating screws. The conventional device may include a horseshoe implant having a plurality of cylindrical holes with smooth inner surfaces and comprise only one stop for the heads of the bone screws to be inserted into them. The placement of five cylindrical holes is oriented within the cage in a non-symmetric manner.

In comparison, the exemplary embodiments differ in many substantial ways from the conventional devices. For example, the exemplary embodiments provide a symmetric orientation of the screw holes, as well as a screw locking mechanism. The exemplary embodiments also provide an angulation/trajectory (e.g., an approximate twenty five degree angulation/trajectory) for preventing pull-out or back-out of the screws that would make placement of all screws in a manner which would lead to maximum stability of the construct within the vertebral space, and obviate the need for external drill guides, and surgeon trajectory angulation guess work.

In another possible conventional device, multiple embodiments of lumbar intervertebral implants may be presented which include one with internally threaded bore holes, another embodiment with a front plate mounted at the front surface of the implant, and another embodiment with the front place displaceably configured to move vertically relative to the implant. In addition, the disclosed preferred borehole axes may be 35-55 degrees. These conventional devices may have four screw perforations that are not aligned four in a row. Two of the screw holes may be laterally placed on the left, one on top of each other, the top one with a superior trajectory, and the bottom with an inferior trajectory. Likewise, two perforations may be placed on the right, one on top of each other, the top one with a superior trajectory and the bottom one with an inferior trajectory. The disclosed screw locking mechanism may be a screw with an external thread matching the internal borehole thread, or spiral springs.

In comparison, the anterior lumbar construct of the exemplary embodiments differs in many substantial ways from these conventional devices. The exemplary embodiments include a single cage construct with four (4) internalized drill guides arranged horizontally in a row. The lateral screw guides/screws are obliquely oriented with the respect to their adjacent medial screw guides/screws. The middle two screws are oriented superiorly, and the lateral left and right screws are oriented inferiorly. This symmetric alignment of screws and orientations within the superior and inferior vertebral bodies (e.g., two middle superiorly projecting screws, and two laterally projecting inferior screws) make the fixation to the superior and inferior vertebral bodies much more symmetric and thus more stable preventing subsidence. In an exemplary embodiment, the cage includes a screw guide having a predetermined trajectory (e.g., an approximate trajectory of 25 degrees or another angulation) that makes placement of all screws equally facile, more amenable to multi-level placement, and diminishes the need for external drill guides. Furthermore, the exemplary screw locking mechanism, which is press-fit to the cage, is unique and differs substantially from the conventional approach of matching screw/cage threads or spiral springs.

FIGS. 3A-3F illustrate three-dimensional views of an exemplary embodiment of a posterior lumbar rectangular intervertebral cage/BDFT construct. In this embodiment, the cage 210 includes indentations 290 on top of the cage 290 that are adjacent to the internal screw guides 270, 280 (FIG. 3F). The indentations 290 contain press-fit leaf springs 220. The cage 210 also includes indentations 12 on both side surfaces of the construct for the prong placement of an implantation tool. The screws 230, 240 perforate and orient in opposing superior and inferior directions.

The cage 210 can include a cavity 250 for bone product placement. The top and bottom portions of the rectangular cage 210 are elliptically contoured to naturally fit into the bi-concave intervertebral disc space (FIG. 3C; side view). The top of cage 210 is a square with equal width and length. The cage 210 includes built-in internalized screw/drill guides 270, 280 having a predetermined angled trajectory (e.g., having an approximate 25 degree angulation), and their axes are not horizontal, but oblique one to the other and very close to each other. Each screw guide/screw 270, 280 occupies one corner of a square, obliquely oriented one to the other (FIG. 3A). This necessary to achieve proper screw penetration in so narrow a posterior lumbar interspace. One of the guides is angled rostrally (superiorly) (e.g., guide 270) and the other caudally (inferiorly) (e.g., guide 280). The intervertebral cages 210 can be designed with internalized screw/drill guides 270, 280 with different angles and/or different positions within the cage 210. Because the tunnel of the screw guide 270, 280 narrows, when the screw 230, 240 is countersunk on top of the cage 210, the screw 230, 240 is preliminarily locked, even in the absence of this locking mechanism. The angle and size of the screws 230, 240 make them amenable to single or multi-level placement. The screw guide exit tunnel 13 adjacent to the bone cavity 250 is illustrated in FIG. 3D. The superior and inferior surfaces or edges can include ridges or the like to facilitate integration and fusion with superior and inferior vertebral bodies. One of these constructs is placed posteriorly into the intervertebral space on the left side, and the other on the right side.

The cage 210 includes a leaf spring screw locking mechanism 220 that can be, for example, press-fit into the indentation 290 adjacent to the internalized screw guides 270, 280 on top of the cage 210. The top of the cage 210 can have an indentation 290 to engage the spring leaf locking mechanism 220. The spring leaf locking mechanism 220 can be manufactured from a variety of materials, such as titanium. When the screws 230, 240 with ratcheted screw heads are turned, the first screw member 230 and the second screw member 240 are locked in a final position by its final turn when the screw head is flush with the surface of the cage 210. The adjacent leaf spring 20 prevents screw back out or pull out by engaging and locking the space between the ratchet teeth (trough) of the screw head when the screws 230, 240 are in their final resting positions. This engagement prevents any rotation of the screw 230, 240 in the opposite direction.

The exemplary embodiment of this novel intervertebral cage 210 is an evolutionary advance and improvement compared to the apparatus illustrated in the aforementioned related applications. The novel cage 210 also is quite unique and different from other conventional locking mechanisms used for other known cervical and lumbar anterior or posterior plate screws. No other conventional posterior lumbar intervertebral cage BDFT/screw constructs are known.

FIGS. 4A-4F illustrate three-dimensional views of an exemplary embodiment of a posterior lumbar elliptical intervertebral cage/BDFT construct. In this embodiment, indentations 290 on top of the cage 210 are adjacent to the internal screw guides 270, 280 (FIG. 4F). The indentations 290 can contain press-fit leaf springs, 220.

The cage 210 also can include indentations or slots 12 on both side surfaces of the cage 210 for insertion of a prong of an implantation tool (see example cage and tool in FIG. 5D; the cage 210 can engage the tool in a similar manner), and more particularly, that engage the distal medial oriented male protuberance of a lateral griper prong of an implantation tool.

The screws 230, 240 perforate and orient in opposing superior and inferior directions. The cage 210 can include a cavity 250 for bone product placement. The entire body of this cage 210 can be elliptical as opposed to the top and bottom portions of the rectangular cage of the previous embodiment 210, and can be contoured when viewed from the side to naturally fit into the bi-concave intervertebral disc space (FIG. 4C).

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